Turbo-molecular pumps are used to draw gasses and suspended particles from chambers that are used to process semiconductor wafers. A conventional pump is illustrated in FIG. 1, and includes a turbine 10 mounted to a pump rotor 12 via mounting bolts 14. The turbine 10 includes fins 16 used to pump the gasses and suspended particles from the chamber (not shown). The tops of the bolts 14 are recessed from the top surface of the turbine 10 in a bolt cavity 18 that has an open end. This conventional design has worked dependably in the past for many years.
Recently, however, conventional pumps having this design have been found to require increased maintenance due to excessive residual process particulate in the wafer chamber, which can result in lower yields. It was discovered that the residual process particulate originates from particles that settle into the bolt cavity 18, and after a certain amount of time and accumulation, are emitted back into the chamber where they can contaminate the wafers being processed therein. This contamination has recently become more problematic because residual process particulate from the bolt cavity 18 are no longer tolerable in many present day wafer processing applications given the reduced process geometries.
There is a need for an improved turbine that prevents excessive residual process particulate.